In industrial settings, control systems are used to monitor and control inventories of industrial and chemical processes and the like. Typically, the control system performs these functions using field devices distributed at key locations in the industrial process coupled to the control circuitry in the control room by a process control loop. The term “field device” refers to any devices that perform a function in a distributor control or process monitoring system used in the measurement, control, and monitoring of industrial processes. Typically, field devices are characterized by their ability to operate outdoors for extended periods of time, such as years. Thus, a field device is able to operate in a variety of climatological extremes, including severe temperature extremes and extremes in humidity. Moreover, field devices are able to function in the presence of significant vibration, such as vibration from adjacent machinery. Further, field devices may operate in the presence of electromagnetic interference.
One example of a field device is a multivariable process fluid pressure transmitter, such as that sold under the trade designation Model 3051 Multivariable Transmitter by Emerson Process Management of Chanhassen, Minn. Multivariable process fluid pressure transmitters can be used for a variety of purposes including the computation and reporting of process fluid mass flow. A multivariable process fluid pressure transmitter will generally have a process fluid differential pressure sensor as well as a static pressure sensor. Measuring both differential pressure and static pressure of the process fluid as the process fluid passes through a differential pressure generator, such as an orifice plate, provides important information regarding process fluid flow.
Multivariable process fluid pressure transmitter performance is sometimes influenced by temperature induced errors. The sources of these temperature-induced errors can be the sensor measurement electronics, sensor oil fill system, and the pressure sensing elements themselves. The performance of a multivariable process fluid pressure transmitter is greatly improved by compensating the output for the temperature effects of the sensor module. This compensation is typically accomplished by characterizing the uncorrected output of the sensor module and developing a mathematical curve fit to produce a corrected sensor module output. Generally, corrected output compensation requires a sensor module design that incorporates an integral temperature sensor. The temperature sensor communicates with the sensor module electronics and provides an output to the electronics known as sensor temperature. This temperature sensor reading is used by the sensor module electronics to compensate the sensor module output.
Providing a multivariable process fluid pressure transmitter with improved temperature compensation abilities would render such devices more accurate. Accuracy is vitally important, and thus improvements in accuracy will benefit the art of process fluid measurement.